Judy, it sounds like the rollers on the bottom of the door aren't on their track.
Try lifting the door straight upward, as if it were going to be removed, then setting it back down; sometimes this will get the rollers in place. You may be able to do one side at a time, or get some help to lift the whole door at once.
Now, just in case....if by chance some of the screws you replaced or altered were the roller adjustment screws that are on the sides of the door down low & accessed through small holes, you may have simply adjusted the rollers too tightly. They only need to be high enough that the door doesn't drag the bottom track, and high enough intruders cannot lift and tilt the door out. Good luck!